Cycle-slip detection method and apparatus, and receiver

ABSTRACT

The present invention provides a cycle-slip detection method and apparatus, and a receiver. If an absolute value of a first difference obtained by subtracting a phase of a first symbol in a k th  training sequence cycle from a phase of a last symbol in a (k−1) th  training sequence cycle in a received signal is greater than a cycle-slip determining threshold, it is determined that a cycle-slip occurs in the k th  or (k−1) th  training sequence cycle. Further, if a second difference obtained by subtracting a phase of the first symbol in the (k+1) th  training sequence cycle from a phase of the last symbol in the k th  training sequence cycle is greater than the cycle-slip determining threshold, and signs of the first difference and the second difference are opposite, it is determined that a cycle-slip occurs in all symbols in the k th  training cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2013/079403, filed Jul. 15, 2013, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of mobile communicationstechnologies, and in particular, to a cycle-slip detection method andapparatus, and a receiver.

BACKGROUND

A phase detector (phase detector) of carrier recovery circuitry (carrierrecovery circuitry) has different stable points (stablepoints)Formultiple phase shift keying (Multiple Phase Shift Keying, MPSK),stable points are given on different constellation points (constellationpoints), where a separation between every two consecutive constellationpoints is 2π/M, and M is a modulation order. This is generally referredto as “2π/M phase ambiguity (phase ambiguity)”. Different de-rotate(de-rotate) logic needs to be used to correct phase ambiguity andde-rotate a symbol (symbol) to a correct constellation, and de-rotatedconstellation points are used for forward error correction (FEC). In acarrier tracking (carrier tracking) process or an acquisition phase(acquisition phase) process, phase estimation generally fluctuates nearthe aforementioned stable points. If noise introduced to a carrierrestore loop exceeds a threshold, phase estimation is pushed to aneighboring stable constellation point. This effect is referred to as acycle-slip (Cycle-Slip), and because the de-rotate logic needs to followstable points, a cycle-slip may cause an error in FEC.

At present, a structure of a conventional receiver is shown in FIG. 1,where a received signal recovers from a signal impairment after passingthrough an equalizer. After being equalized by the equalizer, the signalpasses through a phase estimation apparatus that estimates correspondingphase noise, removes the phase noise from the equalized signal, and thenperforms determining. Because a constellation diagram of a transmitsignal is rotation-invariant at an angle θ relative to the origin (forexample, a quadrature phase shift keying (Quadrature Phase Shift Keying,QPSK) signal and a 16 quadrature amplitude modulation (QuadratureAmplitude Modulation, QAM) signal are rotation-invariant at a 90-degreeangle relative to the origin), a phase φ obtained by means of signalestimation may have a slip of θ relative to an actual phase of thereceived signal, that is, a cycle-slip occurs. In the prior art,training sequences are often interleaved into a received signal to avoidcontinuous bit errors. As shown in FIG. 2, the received signal includesseveral training sequence cycles (including, as shown in FIG. 2,multiple training sequence cycles such as the (k−1)^(th) trainingsequence cycle, the k^(th) training sequence cycle, the (k+1)^(th)training sequence cycle, and the (k+2)^(th) training sequence cycle) ,and each training sequence cycle includes a data (Data) symbol and atraining sequence (Pilot) symbol. The training sequence symbol is agreedby a sending side and a receiving side; therefore, if a cycle-slipoccurs only in a training sequence symbol of a received signal, when anext training sequence symbol arrives, the receiving side may detect thecycle-slip, and then cut off continuous bit errors caused by thecycle-slip. However, if a cycle-slip occurs not only in a trainingsequence symbol, because content of a data symbol is unknown to thereceiving side, a cycle-slip in this case is difficult to detect, and ifthe cycle-slip is not detected and corrected, burst continuous biterrors may occur from a position at which the cycle-slip occurs tillarrival of a next training sequence symbol, which severely degradesperformance of FEC.

SUMMARY

Embodiments of the present invention provide a cycle-slip detectionmethod and apparatus, and a receiver, so as to accurately determine aposition at which a cycle-slip occurs, to avoid a problem of burstcontinuous bit errors in a received signal caused by the cycle-slip.

According to a first aspect, an embodiment of the present inventionprovides a cycle-slip detection method, including:

for a received signal on which phase estimation processing has beenperformed, calculating a first difference by subtracting a phase of thefirst symbol in the k^(th) training sequence cycle from a phase of thelast symbol in the (k−1)^(t) training sequence cycle in the receivedsignal, and determining whether an absolute value of the firstdifference is greater than a set cycle-slip determining threshold, wherethe received signal includes several training sequence cycles, and k isan integer greater than or equal to 2; and if yes, determining that acycle-slip occurs in the k^(th) or (k−1)^(th) training sequence cycle;calculating a second difference by subtracting a phase of the firstsymbol in the (k+1)^(th) training sequence cycle from a phase of thelast symbol in the k^(th) training sequence cycle; and determiningwhether an absolute value of the second difference is greater than theset cycle-slip determining threshold, and whether plus and minus signsof the first difference and the second difference are opposite; if yes,determining that a cycle-slip occurs in all symbols in the k^(th)training cycle; or if not, determining that a cycle-slip occurs in adata symbol in the (k−1)^(th) training sequence cycle, and locating aposition of the cycle-slip.

With reference to the first aspect, in a first possible implementationmanner, the locating a position of the cycle-slip includes:

performing short-time Fourier transform or N_(fft)-point fast Fouriertransform on a phase estimation sequence corresponding to the (k−1)^(th)training sequence cycle, and use a value of the p^(th) frequency as anoutput L_(1−N) of a cycle-slip detection operator corresponding to the(k−1)^(th) training sequence cycle, where N is equal to a length of eachtraining sequence cycle; the p^(th) frequency is a low frequency fromwhich a direct current component has been removed; and the phaseestimation sequence corresponding to the (k−1)^(th) training sequencecycle includes phases that correspond to training sequence symbols anddata symbols in the (k−1)^(th) training sequence cycle;

starting from the first symbol in the (k−1)^(th) training sequencecycle, sequentially comparing a cycle-slip detection operatorcorresponding to each symbol with a cycle-slip detection operatorcorresponding to a next symbol, and when it occurs for the first timethat a cycle-slip detection operator corresponding to a symbol is lessthan a cycle-slip detection operator corresponding to a next symbol,recording the cycle-slip detection operator corresponding to the symbolas L_(idx) _(_) _(start); starting from the last symbol in the(k−1)^(th) training sequence cycle, sequentially comparing a cycle-slipdetection operator corresponding to each symbol with a cycle-slipdetection operator corresponding to a previous symbol, and when itoccurs for the first time that a cycle-slip detection operatorcorresponding to a symbol is less than a cycle-slip detection operatorcorresponding to a previous symbol, recording the cycle-slip detectionoperator corresponding to the symbol as L_(idx) _(_) _(end); and

determining a maximum value L_(idx) between L_(idx) _(_) _(start) andL_(ith) _(_) _(end), and determining that a symbol, corresponding to themaximum value L_(idx), in the (k−1)^(th) training sequence cycle is theposition at which the cycle-slip occurs in the (k−1)^(th) trainingsequence cycle.

With reference to the first aspect and the first possible implementationmanner of the first aspect, in a second possible implementation manner,after the determining that a cycle-slip occurs in all symbols in thek^(th) training cycle, the method further includes:

if the first difference is greater than 0 and the second difference isless than 0, increasing phases corresponding to all the symbols in thek^(th) training sequence cycle by θ; or

if the first difference is less than 0 and the second difference isgreater than 0, decreasing phases corresponding to all the symbols inthe k^(th) training sequence cycle by θ, where

θ is a cycle-slip angle corresponding to a modulation mode of thereceived signal.

With reference to the first possible implementation manner of the firstaspect, in a third possible implementation manner, after the determiningthat a symbol, corresponding to the maximum value L_(idx), in the(k−1)^(th) training sequence cycle is the position at which thecycle-slip occurs in the (k−1)^(th) training sequence cycle, the methodfurther includes:

comparing a phase value φ_(k, idx) corresponding to the symbol in whichthe cycle-slip occurs with a phase φ_(k, idx−1) corresponding to aprevious symbol;

if φ_(k, idx)−φ_(k, idx−1)>0, in the (k−1)^(th) training sequence cycle,decreasing phases φ_(k, idx−N) corresponding to symbols starting fromthe symbol in which the cycle-slip occurs to the last symbol by θ; or

if φ_(k, idx)−φ_(k, idx−)<0, in the (k−1)^(th) training sequence cycle,increasing phases φ_(k, idx−N) correspong to symbols starting from thesymbol in which the cycle-slip occurs to the last symbol by θ, where

θ is a cycle-slip angle corresponding to a modulation mode of thereceived signal.

With reference to the first to the third possible implementation mannersof the first aspect, in a fourth possible implementation manner, whenthe received signal uses a quadrature phase shift keying QPSK or 16quadrature amplitude modulation QAM modulation mode, the cycle-slipdetermining threshold is π/4, and the cycle-slip angle θ is 90 degrees.

According to a second aspect, an embodiment of the present inventionprovides a cycle-slip detection apparatus, where the apparatus includes:

a calculation module, configured to: for a received signal on whichphase estimation processing has been performed, calculate a firstdifference by subtracting a phase of the first symbol in the k^(th)training sequence cycle from a phase of the last symbol in the(k−1)^(th) training sequence cycle in the received signal, where thereceived signal includes several training sequence cycles; and when itis determined that a cycle-slip occurs in the k^(th) or (k−1)^(th)training sequence cycle, calculate a second difference by subtracting aphase of the first symbol in the (k+1)^(th) training sequence cycle froma phase of the last symbol in the k^(th) training sequence cycle, wherek is an integer greater than or equal to 2;

a determining module, configured to determine whether an absolute valueof the first difference is greater than a set cycle-slip determiningthreshold; if yes, determine that a cycle-slip occurs in the k^(th) or(k−1)^(t) training sequence cycle; and determine whether an absolutevalue of the second difference is greater than the set cycle-slipdetermining threshold, and whether plus and minus signs of the firstdifference and the second difference are opposite; if yes, determinethat a cycle-slip occurs in all symbols in the k^(th) training cycle; orif not, determine that a cycle-slip occurs in a data symbol in the(k−1)^(th) training sequence cycle; and

a location module, configured to: when a cycle-slip occurs in a datasymbol in the (k−1)^(th) training sequence cycle, locate a position ofthe cycle-slip.

With reference to the second aspect, in a first possible implementationmanner, the location module includes:

a cycle-slip operator output submodule, configured to perform short-timeFourier transform or N_(fft)-point fast Fourier transform on a phaseestimation sequence corresponding to the (k−1)^(th) training sequencecycle, and use a value of the p^(th) frequency as an output L_(1−N) of acycle-slip detection operator corresponding to the (k−1)^(th) trainingsequence cycle, where N is equal to a length of each training sequencecycle; the p^(th) frequency is a low frequency from which a directcurrent component has been removed; and the phase estimation sequencecorresponding to the (k−1)^(th) training sequence cycle includes phasesthat correspond to training sequence symbols and data symbols in the(k−1)^(th) training sequence cycle; and

a cycle-slip position location submodule, configured to: starting fromthe first symbol in the (k−1)^(th) training sequence cycle, sequentiallycompare a cycle-slip detection operator corresponding to each symbolwith a cycle-slip detection operator corresponding to a next symbol, andwhen it occurs for the first time that a cycle-slip detection operatorcorresponding to a symbol is less than a cycle-slip detection operatorcorresponding to a next symbol, record the cycle-slip detection operatorcorresponding to the symbol asL_(idx) _(_) _(start); starting from thelast symbol in the (k−1)^(th) training sequence cycle, sequentiallycompare a cycle-slip detection operator corresponding to each symbolwith a cycle-slip detection operator corresponding to a previous symbol,and when it occurs for the first time that a cycle-slip detectionoperator corresponding to a symbol is less than a cycle-slip detectionoperator corresponding to a previous symbol, record the cycle-slipdetection operator corresponding to the symbol as L_(idx) _(_) _(end);and deteLittine a maximum value L_(idx) between L_(idx) _(_) _(start)and L_(idx) _(_) _(end), and determine that a symbol, corresponding tothe maximum value L_(idx), in the (k−1)^(th) training sequence cycle isthe position at which the cycle-slip occurs in the (k−1)^(th) trainingsequence cycle.

With reference to the second aspect and the first possibleimplementation manner of the second aspect, in a second possibleimplementation manner, the cycle-slip detection apparatus furtherincludes:

a first cycle-slip correction module, configured to: if the firstdifference is greater than 0 and the second difference is less than 0,increase phases corresponding to all the symbols in the k^(th) trainingsequence cycle by θ; or if the first difference is less than 0 and thesecond difference is greater than 0, decrease phases corresponding toall the symbols in the k^(th) training sequence cycle by θ, where θ is acycle-slip angle corresponding to a modulation mode of the receivedsignal.

With reference to the first possible implementation manner of the secondaspect, in a third possible implementation manner, the cycle-slipdetection apparatus further includes:

a second cycle-slip correction module, configured to compare a phasevalue φ_(k, idx) corresponding to the symbol in which the cycle-slipoccurs with a phase φ_(k, idx−1) corresponding to a previous symbol; ifφ_(k, idx)−φ_(k, idx−)<0, in the (k−1)^(th) training sequence cycle,decrease phases φ_(k, id−N) corresponding to symbols starting from thesymbol in which the cycle-slip occurs to the last symbol by θ; or ifφ_(k, idx)−φ_(idx−1)<0, in the (k−1)^(th) training sequence cycle,increase phases φ_(k, idx−N) corresponding to symbols starting from thesymbol in which the cycle-slip occurs to the last symbol by θ, where θis a cycle-slip angle corresponding to a modulation mode of the receivedsignal.

According to a third aspect, an embodiment of the present inventionprovides a receiver, including: an equalizer, a phase estimationapparatus, and a determining apparatus, and further including theforegoing cycle-slip detection apparatus provided in the embodiments ofthe present invention, where

a signal input end of the cycle-slip detection apparatus is connected toan output end of the phase estimation apparatus, and a signal output endof the cycle-slip detection apparatus is connected to the determiningapparatus.

Beneficial effects of the embodiments of the present invention include:

According to the cycle-slip detection method and apparatus, and thereceiver provided in the embodiments of the present invention, for thek^(th) and (k−1)^(th) training sequence cycles in a received signal onwhich phase estimation processing has been performed, a first differenceis calculated by subtracting a phase of the first symbol in the k^(th)training sequence cycle from a phase of the last symbol in the(k−1)^(th) training sequence cycle; if an absolute value of the firstdifference is greater than a set cycle-slip determining threshold, it isdetermined that a cycle-slip occurs in the k^(th) or (k−1)^(th) trainingsequence cycle. Further, a second difference is calculated bysubtracting a phase of the first symbol in the (k+1)^(th) trainingsequence cycle from a phase of the last symbol in the k^(th) trainingsequence cycle; and it is determined whether the second difference isgreater than the set cycle-slip determining threshold, and whether signsof the first difference and the second difference are opposite; if yes,it is determined that a cycle-slip occurs in all symbols in the k^(th)training cycle; or if not, it is determined that a cycle-slip occurs ina data symbol in the (k−1)^(th) training sequence cycle, and a positionof the cycle-slip is located. According to the cycle-slip detectionmethod provided in the embodiments of the present invention, in a casein which a cycle-slip occurs not only in a training sequence symbol(including that a cycle-slip occurs in a data symbol, and a cycle-slipoccurs in both a training sequence symbol and a data symbol) , accurateidentification and location are implemented, which facilitatescorrecting a cycle-slip, so as to avoid a problem of burst continuousbit errors in a received signal caused by the cycle-slip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of an existing conventionalreceiver;

FIG. 2 is a format diagram of a received signal including severaltraining sequence cycles;

FIG. 3 is a schematic structural diagram of a receiver according to anembodiment of the present invention;

FIG. 4 is a flowchart of a cycle-slip detection method according to anembodiment of the present invention;

FIG. 5 is a flowchart of an instance according to an embodiment of thepresent invention;

FIG. 6 is a first schematic structural diagram of a cycle-slip detectionapparatus according to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a location module accordingto an embodiment of the present invention;

FIG. 8 is a second schematic structural diagram of a cycle-slipdetection apparatus according to an embodiment of the present invention;and

FIG. 9 is a schematic structural diagram of a receiver according to anembodiment of the present invention.

DETAILED DESCRIPTION

The following describes specific implementation manners of a cycle-slipdetection method and apparatus, and a receiver provided in embodimentsof the present invention with reference to the accompanying drawings ofthe specification.

In the cycle-slip detection method provided in the embodiments of thepresent invention, after a phase estimation apparatus in an existingreceiver sends out a signal from which phase noise has been removed, asolution of performing cycle-slip detection on a received signal isadded. As shown in FIG. 3, a cycle-slip detection process depends on anoutput of the phase estimation apparatus, and determining is performedafter the cycle-slip detection is completed. In this way, a problem ofburst continuous bit errors caused by a cycle-slip can be effectivelyavoided.

Specifically, as shown in FIG. 4, a cycle-slip detection method providedin this embodiment of the present invention specifically includes thefollowing steps:

S401. For a received signal on which phase estimation processing hasbeen performed, calculate a first difference by subtracting a phase ofthe first symbol in the k^(th) training sequence cycle from a phase ofthe last symbol in the (k−1)^(th) training sequence cycle, where k is aninteger greater than or equal to 2, and the received signal includesseveral training sequence cycles.

For ease of description, it is assumed that each training sequence cycleincludes N symbols (or in other words, a length of a training sequencecycle is N) , and a phase (that is, an estimated phase obtained by meansof phase estimation processing) corresponding to each symbol in thetraining sequence cycle may be represented by φ_(k,i), and isspecifically represented as a phase corresponding to the i^(th) symbolin the k^(th) training sequence cycle; assuming that in a trainingsequence, M symbols are grouped into one group, i=1˜M represents a phasecorresponding to a training sequence symbol, and i=M+1˜N represents aphase corresponding to a data symbol.

Generally, both a phase corresponding to a training sequence symbol anda phase corresponding to a data symbol are from an output of a phaseestimation apparatus in a receiver (where the phase corresponding to thetraining sequence symbol is based on training sequence estimation, andthe phase corresponding to the data symbol is based on an output of aphase retrieval algorithm) , and a specific phase estimation mannerbelongs to the prior art, which is not described again herein.

S402: Determine whether an absolute value of the first difference isgreater than a set cycle-slip determining threshold; if yes, perform thefollowing step S403; or if not, perform the following step S408.

In step S402, a phase of the last symbol in the (k−1)^(th) trainingsequence cycle is φ_(k−1,N), and a phase of the first symbol in thek^(th) training sequence cycle is φ_(k,i), that is, it is calculatedwhether |φ_(k−1,N)−φ_(k,i)⊕ is greater than the set cycle-slipdetermining threshold, and if yes, it is determined that a cycle-slipoccurs, and the cycle-slip may occur in the k^(th) training sequencecycle or the (k−1)^(th) training sequence cycle.

A cycle-slip threshold is determined according to a modulation mode ofthe received signal, and cycle-slip thresholds corresponding todifferent modulation modes may be different. For QPSK and 16QAMmodulation modes, the cycle-slip threshold may be π/4.

S403. Determine that a cycle-slip occurs in the k^(th) or (k−1)^(th)training sequence cycle; and then further perform the following stepS404.

S404. Calculate a second difference by subtracting a phase of the firstsymbol in the (k+1)^(th) training sequence cycle from a phase of thelast symbol in the k^(th) training sequence cycle.

In step S404, φ_(k,N)−φ_(k+1,1) is calculated to obtain the seconddifference.

S405. Determine whether an absolute value of the second difference isgreater than the set cycle-slip determining threshold, and whether signsof the first difference and the second difference are opposite; if yes,go to the following step S406; or if not, go to the following step S407.

S406. Determine that a cycle-slip occurs in all symbols in the k^(th)training cycle.

S407. Determine that a cycle-slip occurs in a data symbol in the(k−1)^(th) training sequence cycle, and locate a position of thecycle-slip.

S408. End the process.

Preferably, in the foregoing step S407, after it is determined that acycle-slip occurs in a data symbol in the (k−1)^(th) training sequencecycle, the following solution may be used to locate a specific positionof the cycle-slip:

A specific position at which the cycle-slip occurs is actually aposition at which a phase corresponding to each data symbol in the(k−1)^(th) training sequence cycle jump. In this embodiment of thepresent invention, the position at which the cycle-slip occurs may belocated by means of Fourier transform. For example, a manner ofshort-time Fourier transform (STFT, Short-Time Fourier Transform) suchas 4-point short-time Fourier transform may be used, and a value of thesecond frequency is used as an output L_(1−N) of a cycle-slip detectionoperator, where N is equal to a length of the training sequence cycle.

Alternatively, fast Fourier transform (Fast Fourier Transform, FFT) suchas N_(fft)-point fast Fourier transform may be used, where N_(fft) is aquantity of points in fast Fourier transform, and a value of the p^(th)frequency is used as an output L_(1−N) of a cycle-slip detectionoperator, where the p^(th) frequency may be a low frequency from which adirect current component has been removed. Preferably, for theN_(fft)-point fast Fourier transform, p=N_(fft)/2 or (N_(fft)/2)+2.

The output L_(1−N) of the cycle-slip detection operator includes Nvalues that are one-to-one corresponding to all symbols in the(k−1)^(th) training sequence cycle.

Starting from the first symbol in the (k−1)^(th) training sequencecycle, a cycle-slip detection operator corresponding to each symbol issequentially compared with a cycle-slip detection operator correspondingto a next symbol, and when it occurs for the first time that acycle-slip detection operator corresponding to a symbol is less than acycle-slip detection operator corresponding to a next symbol, a positioncorresponding to the symbol is recorded as idx_start, and acorresponding cycle-slip detection operator is recorded as L_(idx) _(_)_(start).

Starting from the last symbol in the (k−1)^(th) training sequence cycle,a cycle-slip detection operator corresponding to each symbol issequentially compared with a cycle-slip detection operator correspondingto a previous symbol, and when it occurs for the first time that acycle-slip detection operator corresponding to a symbol is less than acycle-slip detection operator corresponding to a previous symbol, aposition corresponding to the symbol is recorded as idx_end, and acorresponding cycle-slip detection operator is recorded as L_(idx) _(_)_(end).

A maximum value L_(idx) between L_(idx) _(_) _(start) and L_(idx) _(_)_(end) is found in the output L_(1−N) of the cycle-slip detectionoperator, and a symbol, corresponding to the maximum value, in the(k−1)^(th) training sequence cycle is the position at which thecycle-slip occurs in the training sequence cycle.

The foregoing processes of determining L_(idx) _(_) _(start) and L_(idx)_(_) _(end) are independent of each other, and may be performedsequentially or may be performed simultaneously.

Further, if 4-point short-time Fourier transform is performed on a phaseestimation sequence φ_(k−1,1˜N) corresponding to the (k−1)^(th) trainingsequence cycle, and a value of the second frequency is used as an outputL_(1−N) of the cycle-slip detection operator, phases φ_(k−1,1˜N)corresponding to all symbols in the (k−1)^(th) training sequence cycleare first arranged as a φ(n) in chronological order, where n=N*(k−1)+i,i=1˜N, and N is a length of a training sequence cycle (that is, aninterval between neighboring training sequences in the received signal).N=128 is used as an example:

When arrangement is performed in chronological order, a correspondencebetween φ_(k,i) and φ(n) is as follows:

φ(1˜128) is corresponding to φ_(1,1˜128);

φ(129˜256) is corresponding to φ_(2,1˜128);

φ(257˜384) is corresponding to φ_(31˜128);

When the value of the second frequency is used as an output of thecycle-slip detection operator, the output of the cycle-slip detectionoperat L(n)=φ(n−1)−φ(n+1))̂2+φ(n−2)−φ(n))̂2.

Corresponding to φ_(k−1,1˜N), the output of the cycle-slip detectionoperator includes 128 values, that is, L_(1˜128), which are one-to-onecorresponding to all symbols in the (k−1)^(th) training sequence cyclein which the cycle-slip occurs.

According to the foregoing method provided in this embodiment of thepresent invention, after it is determined that a cycle-slip occurs, nomatter the cycle-slip occurs in the k^(th) cycle or in the (k−1)^(th)cycle, a phase corresponding to a position at which the cycle-slipoccurs needs to be rotated to correct the cycle-slip, and preferably,the following manner may be used to correct the cycle-slip:

After the foregoing S406, that is, after it is determined that acycle-slip occurs in all symbols in the k^(th) training cycle, if thefirst difference is greater than 0 and the second difference is lessthan 0 (that is, φ_(k−1,N)−φ_(k,1)>0, and φ_(k,N)−φ_(k+1,1)<0), phasecorresponding to all the symbols in the k^(th) training sequence cycleare increased by θ (that is, φ_(k−3˜N)=φ_(k,1˜N)+θ).

If the first difference is less than 0 and the second difference isgreater than 0 (that is, φ_(k−1,N)−φ_(k,i)<0, and φ_(k,N)−φ_(k+1,1)>0),phases corresponding to all the symbols in the k^(th) training sequencecycle are decreased by θ (that is,φ_(k,1−N)−θ).

After the foregoing S407, that is, after it is determined that aposition of a symbol corresponding to the maximum value L_(idx) is theposition at which the cycle-slip occurs, a phase value φ_(k, idx)corresponding to the symbol in which the cycle-slip occurs is comparedwith a phase value φ_(k, idx−1) corresponding to a previous symbol.

If φ_(k, idx)−φ_(k, idx−1)>0, in the (k−1)^(th) training sequence cycle,phases φ_(k, idx˜N) corresponding to symbols starting from the symbol inwhich the cycle-slip occurs to the last symbol are decreased by θ.

If φ_(k, idx)−φ_(k, idx−)<0, in the (k−1)^(th) training sequence cycle,phases φ_(k, idx˜N) corresponding to symbols starting from the symbol inwhich the cycle-slip occurs to the last symbol are increased by θ.

In the foregoing cycle-slip correction process, θ is a cycle-slip anglecorresponding to a modulation mode of the received signal, and for eachmodulation mode, a constellation diagram of a transmit signal (which isa received signal for a signal receive end) is fixed, where theconstellation diagram is rotation-invariant at an angle θ relative tothe origin, and θ is the cycle-slip angle. In other words, a specificvalue of θ is a minimum angle by which a constellation diagram of asignal is rotated about the origin so that the constellation diagramafter rotation overlaps the original constellation diagram. For example,in a case in which a signal uses a QPSK or 16QAM modulation mode, thecycle-slip angle e is 90 degrees, and in a case in which a transmitsignal uses an 8PSK modulation mode, the cycle-slip angle is π/4 .Specific cycle-slip angles may be different according to differentmodulation modes.

With a simple process, the following describes the foregoing cycle-slipdetection method provided in this embodiment of the present invention byusing an example in which the received signal uses a QPSK or 16QAMmodulation mode, and the cycle-slip angle θ is 90 degrees.

As shown in FIG. 5, the process includes:

Step 1: When the k^(th) training sequence cycle arrives, compareφ_(k−1,N) and φ_(k,i), and if

${{{\phi_{{k - 1},N} - \phi_{k,1}}} > \frac{\pi}{4}},$

determine that a cycle-slip occurs;

otherwise, determine that no cycle-slip occurs, where if it isdetermined that a cycle-slip occurs, the cycle-slip may occur in the(k−1)^(th) training sequence cycle, or the k^(th) training sequencecycle.

Step 2: If it is determined that

${{{\phi_{{k - 1},N} - \phi_{k,1}}} > \frac{\pi}{4}},$

continue to compare φ_(k,N) and φ_(k+1,1)and if

${{{\phi_{k,N} - \phi_{{k + 1},1}}} > \frac{\pi}{4}},$

perform the following step 3; otherwise, perform the following step 7.

Step 3: Next, determine whether (φ_(k−1,N)−φ_(k,i)) and(φ_(k,N)−φ_(k+1,1)) meet: (φ_(k−1,N)−φ_(k,i))>0 (φ_(k,N)−φ_(k+1,1))>0,and if yes, perform step 5; otherwise go to step 4.

Step 4: Next, determine whether (φ_(k−1,N)−φ_(k,i)) and(φ_(k,N)−φ_(k+1,1)) meet: (φ_(k−1,N)−φ_(k,i)) and (φ_(k,N)−φ_(k+1,1))>0,and if yes, peform step 5; otherwise go to step 7.

Step 5: Increase φ_(k,1−N) by 90 degrees, that is,φ_(k,1−N)=φ_(k,1−N)+90°.

Step 6: Decrease φ_(k,1−N) by 90 degrees, that is,φ_(k,1−N)=φ_(k,1−N)−90°.

Step 7: Detect a position of the cycle-slip in the (k−1)^(th) cycle, andcorrect the cycle-slip.

Actually, in the foregoing step 3 and step 4, it is already determinedthat a cycle-slip occurs in all symbols in the k^(th) training sequencecycle.

In the foregoing step 7, the method for detecting the position of thecycle-slip in the (k−1)^(th) cycle and correcting the cycle-slip hasbeen described in detail above, and is not described herein again.

Based on the same invention concept, an embodiment of the presentinvention further provides a cycle-slip detection apparatus and areceiver. Principles of the apparatus and the receiver for solving theproblem are similar to that of the foregoing cycle-slip detectionmethod; therefore, for implementation of the apparatus and the receiver,reference may be made to the implementation of the foregoing method, andrepeated parts are not described again.

As shown in FIG. 6, a first possible implementation manner of thecycle-slip detection apparatus provided in this embodiment of thepresent invention includes:

a calculation module 601, configured to: for a received signal on whichphase estimation processing has been performed, calculate a firstdifference by subtracting a phase of the first symbol in the k^(th)training sequence cycle from a phase of the last symbol in the(k−1)^(th) training sequence cycle in the received signal, where thereceived signal includes several training sequence cycles; and when itis determined that a cycle-slip occurs in the k^(th) or (k−1)^(th)training sequence cycle, calculate a second difference by subtracting aphase of the first symbol in the (k+1)^(th) training sequence cycle froma phase of the last symbol in the k^(th) training sequence cycle, wherek is an integer greater than or equal to 2;

a determining module 602, configured to determine whether an absolutevalue of the first difference is greater than a set cycle-slipdetermining threshold; if yes, determine that a cycle-slip occurs in thek^(th) or (k−1)^(th) training sequence cycle; and determine whether anabsolute value of the second difference is greater than the setcycle-slip determining threshold, and whether signs of the firstdifference and the second difference are opposite; if yes, determinethat a cycle-slip occurs in all symbols in the k^(th) training cycle; orif not, determine that a cycle-slip occurs in a data symbol in the(k−1)^(th) training sequence cycle; and

a location module 603, configured to: when a cycle-slip occurs in a datasymbol in the (k−1)^(th) training sequence cycle, locate a position ofthe cycle-slip.

Further, as shown in FIG. 7, the foregoing location module 603 includes:

a cycle-slip operator output submodule 6031, configured to performshort-time Fourier transform or N_(fft)-point fast Fourier transform ona phase estimation sequence corresponding to the (k−1)^(th) trainingsequence cycle, and use a value of the p^(th)frequency as an outputL_(1−N) of a cycle-slip detection operator corresponding to the(k−1)^(th) training sequence cycle, where N is equal to a length of eachtraining sequence cycle; the p^(th) frequency is a low frequency fromwhich a direct current component has been removed; and the phaseestimation sequence corresponding to the (k−1)^(th) training sequencecycle includes phases that correspond to training sequence symbols anddata symbols in the (k−1)^(th) training sequence cycle; and

a cycle-slip position location submodule 6032, configured to: startingfrom the first symbol in the (k−1)^(th) training sequence cycle,sequentially compare a cycle-slip detection operator corresponding toeach symbol with a cycle-slip detection operator corresponding to a nextsymbol, and when it occurs for the first time that a cycle-slipdetection operator corresponding to a symbol is less than a cycle-slipdetection operator corresponding to a next symbol, record the cycle-slipdetection operator corresponding to the symbol as L_(idx) _(_) _(start);starting from the last symbol in the (k−1)^(th) training sequence cycle,sequentially compare a cycle-slip detection operator corresponding toeach symbol with a cycle-slip detection operator corresponding to aprevious symbol, and when it occurs for the first time that a cycle-slipdetection operator corresponding to a symbol is less than a cycle-slipdetection operator corresponding to a previous symbol, record thecycle-slip detection operator corresponding to the symbol as L_(idx)_(_) _(end); and determine a maximum value L_(idx) between L_(idx) _(_)_(start) and L_(idx) _(_) _(end), and determine that a symbol,corresponding to the maximum value L_(idx), in the (k−1)^(th) trainingsequence cycle is the position at which the cycle-slip occurs in the(k−1)^(th) training sequence cycle.

Further, the cycle-slip output submodule 6032 is specifically configuredto perform 4-point short-time Fourier transform on a phase estimationsequence φ_(k−1,1˜N) corresponding to the (k−1)^(th) training sequencecycle, and use a value of the second frequency as an output L_(1˜N) ofthe cycle-slip detection operator, whereL(n)=(φ(n−1)−φ(n+1))̂2+(φ(n−2)−φ(n))̂2, and φ(n) is obtained arranging thephase estimation sequence φ_(k−1,1˜N) in chronological order, wheren=N*(k−1)+i, i=1˜N, and N is a length of each training sequence cycle.

Further, as shown in FIG. 6, the cycle-slip detection apparatus furtherincludes: a first cycle-slip correction module 604, configured to : ifthe first difference is greater than 0 and the second difference is lessthan 0, increase phases corresponding to all the symbols in the k^(th)training sequence cycle by θ; or if the first difference is less than 0and the second difference is greater than 0, decrease phasescorresponding to all the symbols in the k^(th) training sequence cycleby θ, where θ is a cycle-slip angle corresponding to a modulation modeof the received signal.

Further, as shown in FIG. 6, the cycle-slip detection apparatus furtherincludes: a second cycle-slip correction module 605, configured tocompare a phase value φ_(k, idx) corresponding to the symbol in whichthe cycle-slip occurs with a phase φ_(k, idx−1) corresponding to aprevious symbol; if φ_(k, idx)−φ_(k, idx)>0, in the (k−1)^(th) trainingsequence cycle, decrease phases φ_(k, idx˜N) corresponding to symbolsstarting from the symbol in which the cycle-slip occurs to the lastsymbol by θ; or if φ_(k, idx)−φ_(idx−)<0, in the (k−1)^(th) trainingsequence cycle, increase phases φ_(k, idx−N) corresponding to symbolsstarting from the symbol in which the cycle-slip occurs to the lastsymbol by θ, where θ is a cycle-slip angle corresponding to a modulationmode of the received signal.

As shown in FIG. 8, a second possible implementation manner of thecycle-slip detection apparatus provided in this embodiment of thepresent invention includes:

a processor 801, configured to: fora received signal on which phaseestimation processing has been performed, calculate a first differenceby subtracting a phase of the first symbol in the k^(th) trainingsequence cycle from a phase of the last symbol in the (k−1)^(th)training sequence cycle in the received signal, where the receivedsignal includes several training sequence cycles; when it is determinedthat a cycle-slip occurs in the k^(th) or (k−1)^(th) training sequencecycle, calculate a second difference by subtracting a phase of the firstsymbol in the (k+1)^(th) training sequence cycle from a phase of thelast symbol in the k^(th) training sequence cycle, where k is an integergreater than or equal to 2; if an absolute value of the first differenceis greater than a set cycle-slip determining threshold, determine that acycle-slip occurs in the k^(th) or (k−1)^(th) training sequence cycle;if an absolute value of the second difference is greater than the setcycle-slip determining threshold, and signs of the first difference andthe second difference are opposite, determine that a cycle-slip occursin all symbols in the k^(th) training cycle; or if not, determine that acycle-slip occurs in a data symbol in the (k−1)^(th) training sequencecycle;

a memory 802, configured to store the first difference and the seconddifference that are obtained through calculation; and a comparator 803,configured to determine whether the absolute value of the firstdifference is greater than the set cycle-slip determining threshold; anddetermine whether the absolute value of the second difference is greaterthan the set cycle-slip determining threshold, and whether plus andminus signs of the first difference and the second difference areopposite.

As shown in FIG. 9, an embodiment of the present invention furtherprovides a receiver, including: an equalizer 901, a phase estimationapparatus 902, a determining apparatus 903, and the foregoing cycle-slipdetection apparatus 904 provided in the embodiments of the presentinvention, where a signal input end of the cycle-slip detectionapparatus 904 is connected to an output end of the phase estimationapparatus 902, and a signal output end of the cycle-slip detectionapparatus 904 is connected to the determining apparatus 903. Functionsof and mutual connection structures among the equalizer 901, the phaseestimation apparatus 902, and the determining apparatus 903 are the sameas those in the prior art, and are not described again herein

According to the cycle-slip detection method and apparatus, and thereceiver provided in the embodiments of the present invention, for thek^(th) and (k−1)^(th) training sequence cycles in a received signal onwhich phase estimation processing has been performed, a first differenceis calculated by subtracting a phase of the first symbol in the k^(th)training sequence cycle from a phase of the last symbol in the(k−1)^(th) training sequence cycle; if an absolute value of the firstdifference is greater than a set cycle-slip determining threshold, it isdetermined that a cycle-slip occurs in the k^(th) or (k−1)^(th) trainingsequence cycle. Further, a second difference is calculated bysubtracting a phase of the first symbol in the (k+l)^(th) trainingsequence cycle from a phase of the last symbol in the k^(th) trainingsequence cycle; and it is determined whether the second difference isgreater than the set cycle-slip determining threshold, and whether signsof the first difference and the second difference are opposite; if yes,it is determined that a cycle-slip occurs in all symbols in the k^(th)training cycle; or if not, it is determined that a cycle-slip occurs ina data symbol in the (k−1)^(th) training sequence cycle, and a positionof the cycle-slip is located. According to the cycle-slip detectionmethod provided in the embodiments of the present invention, in a case(including that a cycle-slip occurs in a data symbol, and a cycle-slipoccurs in both a training sequence symbol and a data symbol) in which acycle-slip occurs not only in a training sequence symbol in a receivedsignal, accurate identification and location are implemented, whichfacilitates correcting a cycle-slip, so as to avoid a problem of burstcontinuous bit errors in a received signal caused by the cycle-slip.

According to the description of the foregoing implementation manners, aperson skilled in the art may clearly understood that the embodiments ofthe present invention may be implemented by hardware, or may beimplemented in a manner of software plus a necessary universal hardwareplatform. Based on such an understanding, the technical solutions of theembodiments of the present invention may be expressed in a form of asoftware product, where the software product may be stored in anon-volatile storage medium (which may be a CD-ROM, a USB flash disk, aremovable hard disk, or the like) , and include several instructions formaking a computer device (which may be a personal computer, a server, anetwork device, or the like) to execute the method of the embodiments ofthe present invention.

A person skilled in the art may understand that the accompanyingdrawings are merely schematic diagrams of exemplary embodiments, andmodules or processes in the accompanying drawings are not necessarilyrequired for implementing the present invention.

A person skilled in the art may understand that the modules in theapparatuses provided in the embodiments may be arranged in theapparatuses in a distributed manner according to the description of theembodiments, or may be arranged in one or more apparatuses that aredifferent from those described in the embodiments. The modules in theforegoing embodiments maybe combined into one module, or split into aplurality of submodules.

The sequence numbers of the foregoing embodiments of the presentinvention are merely for illustrative purposes, and are not intended toindicate priorities of the embodiments.

Obviously, a person skilled in the art can make various modificationsand variations to the present invention without departing from thespirit and scope of the present invention. The present invention isintended to cover these modifications and variations provided that theyfall within the scope of protection defined by the following claims andtheir equivalent technologies.

What is claimed is:
 1. A cycle-slip detection method, comprising: for areceived signal on which phase estimation processing has been performed,calculating a first difference by subtracting a phase of a first symbolin a k^(th) training sequence cycle from a phase of a last symbol in a(k−1)^(th) training sequence cycle in the received signal, anddetermining whether an absolute value of the first difference is greaterthan a set cycle-slip determining threshold, wherein the received signalcomprises several training sequence cycles, and k is an integer greaterthan or equal to 2; and if yes, determining that a cycle-slip occurs inthe k^(th) or (k−1)^(th) training sequence cycle; calculating a seconddifference by subtracting a phase of the first symbol in the (k+1)^(th)training sequence cycle from a phase of the last symbol in the k^(th)training sequence cycle; and determining whether an absolute value ofthe second difference is greater than the set cycle-slip determiningthreshold, and whether plus and minus signs of the first difference andthe second difference are opposite; if yes, determining that acycle-slip occurs in all symbols in the k^(th) training cycle; or ifnot, determining that a cycle-slip occurs in a data symbol in the(k−1)^(th) training sequence cycle, and locating a position of thecycle-slip.
 2. The method according to claim 1, wherein locating aposition of the cycle-slip comprises: performing short-time Fouriertransform or ^(N)ffi -point fast Fourier transform on a phase estimationsequence corresponding to the (k−1)^(th) training sequence cycle, andusing a value of the p^(th) frequency as an output L_(1−N) of acycle-slip detection operator corresponding to the (k−1)^(th) trainingsequence cycle, wherein N is equal to a length of each training sequencecycle; the p^(th) frequency is a low frequency from which a directcurrent component has been removed; and the phase estimation sequencecorresponding to the (k−1)^(th) training sequence cycle comprises phasesthat correspond to training sequence symbols and data symbols in the(k−1)^(th) training sequence cycle; starting from the first symbol inthe (k−1)^(th) training sequence cycle, sequentially comparing acycle-slip detection operator corresponding to each symbol with acycle-slip detection operator corresponding to a next symbol, and whenit occurs for the first time that a cycle-slip detection operatorcorresponding to a symbol is less than a cycle-slip detection operatorcorresponding to a next symbol, recording the cycle-slip detectionoperator corresponding to the symbol as L_(idx) _(_) _(start); startingfrom the last symbol in the (k−1)^(th) training sequence cycle,sequentially comparing a cycle-slip detection operator corresponding toeach symbol with a cycle-slip detection operator corresponding to aprevious symbol, and when it occurs for the first time that a cycle-slipdetection operator corresponding to a symbol is less than a cycle-slipdetection operator corresponding to a previous symbol, recording thecycle-slip detection operator corresponding to the symbol L_(idx) _(_)_(end); and determining a maximum value L_(idx) between L_(idx) _(_)_(start) and L_(idx) _(_) _(end), and determining that a symbol,corresponding to the maximum value L_(idx), in the (k−1)^(th) trainingsequence cycle is the position at which the cycle-slip occurs in the(k−1)^(th) training sequence cycle.
 3. The method according to claim 1,wherein after determining that a cycle-slip occurs in all symbols in thek^(th) training cycle, the method further comprises : if the firstdifference is greater than 0 and the second difference is less than 0,increasing phases corresponding to all the symbols in the k^(th)training sequence cycle by θ; or if the first difference is less than 0and the second difference is greater than 0, decreasing phasescorresponding to all the symbols in the k^(th) training sequence cycleby θ; and wherein θ is a cycle-slip angle corresponding to a modulationmode of the received signal.
 4. The method according to claim 2, whereinafter determining that a symbol, corresponding to the maximum valueL_(idx), in the (k−1)^(th) training sequence cycle is the position atwhich the cycle-slip occurs in the (k−1)^(th) training sequence cycle,the method further comprises : comparing a phase value φ_(k, idx)corresponding to the symbol in which the cycle-slip occurs with a phaseφ_(k, idx−1) corresponding to a previous symbol; and ifφ_(k, idx)−φ_(k, idx−)>0, in the (k−1)^(th) training sequence cycle,decreasing phases φ_(k, idx˜N) corresponding to symbols startingl fromthe symbol in which the cycle-slip occurs to the last symbol by θ; or ifφ_(k, idx)−φ_(k, idx−1)<0, in the (k−1)^(th) training sequence cycle,increasing phases φ_(k, idx˜N) corresponding to symbols starting fromthe symbol in which the cycle-slip occurs to the last symbol by θ; andwherein 0 is a cycle-slip angle corresponding to a modulation mode ofthe received signal.
 5. The method according to claim 1, wherein whenthe received signal uses a quadrature phase shift keying (QPSK) or 16quadrature amplitude modulation (QAM) modulation mode, the cycle-slipdetermining threshold is π/4, and the cycle-slip angle θ is 90 degrees.6. A cycle-slip detection apparatus, comprising: a calculation module,configured to: for a received signal on which phase estimationprocessing has been performed, calculate a first difference bysubtracting a phase of a first symbol in a k^(th) training sequencecycle from a phase of a last symbol in a (k−1)^(th) training sequencecycle in the received signal, wherein the received signal comprisesseveral training sequence cycles, and when it is determined that acycle-slip occurs in the k^(th) or (k−1)^(th) training sequence cycle,calculate a second difference by subtracting a phase of the first symbolin the (k+1)^(th) training sequence cycle from a phase of the lastsymbol in the k^(th) training sequence cycle, wherein k is an integergreater than or equal to 2; a determining module, configured to :determine whether an absolute value of the first difference is greaterthan a set cycle-slip determining threshold; if yes, determine that acycle-slip occurs in the k^(th) or (k−1)^(th) training sequence cycle;and determine whether an absolute value of the second difference isgreater than the set cycle-slip determining threshold, and whether plusand minus signs of the first difference and the second difference areopposite; if yes, determine that a cycle-slip occurs in all symbols inthe k^(th) training cycle; or if not, determine that a cycle-slip occursin a data symbol in the (k−1)^(th) training sequence cycle; and alocation module, configured to: when a cycle-slip occurs in a datasymbol in the (k−1)^(th) training sequence cycle, locate a position ofthe cycle-slip.
 7. The apparatus according to claim 6, wherein thelocation module comprises: a cycle-slip operator output submodule,configured to perform short-time Fourier transform or N_(fft)-point fastFourier transform on a phase estimation sequence corresponding to the(k−1)^(th) training sequence cycle, and use a value of the p^(th)frequency as an output L_(1˜N) of a cycle-slip detection operatorcorresponding to the (k−1)^(th) training sequence cycle, wherein N isequal to a length of each training sequence cycle, the p^(th) frequencyis a low frequency from which a direct current component has beenremoved, and the phase estimation sequence corresponding to the(k−1)^(th) training sequence cycle comprises phases that correspond totraining sequence symbols and data symbols in the (k−1)^(th) trainingsequence cycle; and a cycle-slip position location submodule, configuredto : starting from the first symbol in the (k−1)^(th) training sequencecycle, sequentially compare a cycle-slip detection operatorcorresponding to each symbol with a cycle-slip detection operatorcorresponding to a next symbol, and when it occurs for the first timethat a cycle-slip detection operator corresponding to a symbol is lessthan a cycle-slip detection operator corresponding to a next symbol,record the cycle-slip detection operator corresponding to the symbol asL_(idx) _(_) _(start); starting from the last symbol in the (k−1)^(th)training sequence cycle, sequentially compare a cycle-slip detectionoperator corresponding to each symbol with a cycle-slip detectionoperator corresponding to a previous symbol, and when it occurs for thefirst time that a cycle-slip detection operator corresponding to asymbol is less than a cycle-slip detection operator corresponding to aprevious symbol, record the cycle-slip detection operator correspondingto the symbol as L_(ith) _(_) _(end); and determine a maximum valueL_(idx) between L_(idx) _(_) _(start) and L_(idx) _(_) _(end), anddetermine that a symbol, corresponding to the maximum value L_(idx), inthe (k−1)^(th) training sequence cycle is the position at which thecycle-slip occurs in the (k−1)^(th) training sequence cycle.
 8. Theapparatus according to claim 6, further comprising a first cycle-slipcorrection module, configured to: if the first difference is greaterthan 0 and the second difference is less than 0, increase phasescorresponding to all the symbols in the k^(th) training sequence cycleby θ; or if the first difference is less than 0 and the seconddifference is greater than 0, decrease phases corresponding to all thesymbols in the k^(th) training sequence cycle by θ; and wherein θ is acycle-slip angle corresponding to a modulation mode of the receivedsignal.
 9. The apparatus according to claim 7, further comprising asecond cycle-slip correction module, configured to: compare a phasevalue φ_(k, idx) corresponding to the symbol in which the cycle-slipoccurs with a phase φ_(k, idx−1) corresponding to a previous symbol; andif φ_(k, idx)−φ_(idx−)>0, in the (k−1)^(th) training sequence cycle,decrease phases φ_(k, idx˜N) corresponding to symbols starting from thesymbol in which the cycle-slip occurs to the last symbol by θ; or ifφ_(k, idx)−φ_(k, idx−)<0, in the (k−1)^(th) training sequence cycle,increase phases φ_(k, idx˜N) corresponding to symbols starting from thesymbol in which the cycle-slip occurs to the last symbol by θ; andwherein θ is a cycle-slip angle corresponding to a modulation mode ofthe received signal.
 10. A cycle-slip detection apparatus comprising: amemory; and a processor coupled to the memory and configured withprocessor-executable instructions to perform the following: for areceived signal on which phase estimation processing has been performed,calculating a first difference by subtracting a phase of the firstsymbol in the k^(th) training sequence cycle from a phase of the lastsymbol in the (k−1)^(th) training sequence cycle in the received signal,and determining whether an absolute value of the first difference isgreater than a set cycle-slip determining threshold, wherein thereceived signal comprises several training sequence cycles, and k is aninteger greater than or equal to 2; and if yes, determining that acycle-slip occurs in the k^(th) or (k−1)^(th) training sequence cycle;calculating a second difference by subtracting a phase of the firstsymbol in the (k+1)^(th) training sequence cycle from a phase of thelast symbol in the k^(th) training sequence cycle; and determiningwhether an absolute value of the second difference is greater than theset cycle-slip determining threshold, and whether plus and minus signsof the first difference and the second difference are opposite; if yes,determining that a cycle-slip occurs in all symbols in the k^(th)training cycle; or if not, determining that a cycle-slip occurs in adata symbol in the (k−1)^(th) training sequence cycle, and locating aposition of the cycle-slip.
 11. The apparatus according to claim 10,wherein the processor is configured with processor-executableinstructions to perform the following: performing short-time Fouriertransform or N_(fft)-point fast Fourier transform on a phase estimationsequence corresponding to the (k−1)^(th) training sequence cycle, andusing a value of the p^(th) frequency as an output L_(1˜N) of acycle-slip detection operator corresponding to the (k−1)^(th) trainingsequence cycle, wherein N is equal to a length of each training sequencecycle; the p^(th) frequency is a low frequency from which a directcurrent component has been removed; and the phase estimation sequencecorresponding to the (k−1)^(th) training sequence cycle comprises phasesthat correspond to training sequence symbols and data symbols in the(k−1)^(th) training sequence cycle; starting from the first symbol inthe (k−1)^(th) training sequence cycle, sequentially comparing acycle-slip detection operator corresponding to each symbol with acycle-slip detection operator corresponding to a next symbol, and whenit occurs for the first time that a cycle-slip detection operatorcorresponding to a symbol is less than a cycle-slip detection operatorcorresponding to a next symbol, recording the cycle-slip detectionoperator corresponding to the symbol as L_(idx) _(_) _(start); startingfrom the last symbol in the (k−1)^(th) training sequence cycle,sequentially comparing a cycle-slip detection operator corresponding toeach symbol with a cycle-slip detection operator corresponding to aprevious symbol, and when it occurs for the first time that a cycle-slipdetection operator corresponding to a symbol is less than a cycle-slipdetection operator corresponding to a previous symbol, recording thecycle-slip detection operator corresponding to the symbol as L_(idx)_(_) _(end); and determining a maximum value L_(idx) between L_(idx)_(_) _(start) and L_(idx) _(_) _(end), and determining that a symbol,corresponding to the maximum value L_(idx), in the (k−1)^(th) trainingsequence cycle is the position at which the cycle-slip occurs in the(k−1)^(th) training sequence cycle.